Heretofore, an electric power steering apparatus is known as one example of electrical control systems that are supplied from an automotive battery as a power supply. Although the electric power steering apparatus is an apparatus that controls energizing amount to a motor depending on a steering state of a steering wheel and provide a steering assist torque (an assist force), its electricity consumption is considerably high. For this reason, in the case that capability of a battery dropped (hereinafter referred to as “degradation”), there is a possibility that the energizing amount to the motor which generates the steering assist torque is limited and a given steering torque is not obtained, and there is also a possibility of causing a reduction in power-supply voltage to other electrical control systems that operate simultaneously. Therefore, before becoming such a situation, it is important to detect battery degradation in advance and prompt battery exchange for a driver.
Here, as one example of electrical control systems, a general configuration of an electric power steering apparatus will be described with reference to FIG. 1. A column shaft 2 connected to a steering wheel (handle) 1 is connected to tlc rods 6 of steered wheels through reduction gears 3, universal joints 4A and 4B, and a rack and pinion mechanism 5. The column shaft 2 is provided with a torque sensor 10 for detecting a steering torque Tr of the steering wheel 1, and a motor 20 for assisting the steering force of the steering wheel 1 is connected to the column shaft 2 through the reduction gears 3. Electric power is supplied to an ECU (Electronic Control Unit) 100 for controlling the electric power steering apparatus etc. from a battery 14, and an ignition signal IG is inputted into the ECU 100 through an ignition key 11. A calculation and control section 110 within the ECU 100 calculates a current command value I of an assist command based on the steering torque Tr detected by the torque sensor 10 and a velocity Vr detected by a velocity sensor 12, and controls the motor 20 based on the calculated current command value I. In the case of the vector control, the current command value I comprises a q-axis current command value Iq with respect to a q-axis for controlling a torque which is a coordinate axis of a rotor magnet and a d-axis current command value Id with respect to a d-axis for controlling the strength of a magnetic field, and since the q-axis and the d-axis have a relation of 90-degree, current corresponding to each axis is controlled by that vector.
Furthermore, the velocity Vr can be obtained from a CAN (Controller Area Network) and then inputted into the ECU 100. It is also possible to additionally use a steering angle θ obtained from a steering angle sensor for calculating the current command value I.
Configuration and operations of the ECU 100 that drives and controls the motor 20 will be described with respect to the vector control.
In the case of the vector control, the motor 20 is a brushless DC motor (in this embodiment, a three-phase brushless DC motor), since a rotational angle (the steering angle) θ and a motor angular velocity ω of the motor 20 are necessary for control, a resolver 21 as an angle detecting element is connected to the motor 20, and the ECU 100 is provided with a resolver-to-digital converting circuit (RDC) 101 that converts an alternating-current resolver detection signal RS into a digital steering angle θ and a digital motor angular velocity ω. The ECU 100 mainly comprises functions (software) of a CPU (also including an MPU (Micro Processor Unit), an MCU (Micro Controller Unit) and so on), and comprises the calculation and control section 110 that performs necessary calculation processing and total control. The calculation and control section 110 obtains the q-axis current command value Iq and the d-axis current command value Id by calculations based on the steering torque Tr from the torque sensor 10, the velocity Vr from the velocity sensor 12 (or the CAN), and the steering angle θ and the motor angular velocity ω from the RDC 101, and inputs the q-axis current command value Iq and the d-axis current command value Id into a motor driving control section 120 to perform the vector control. The ignition signal IG from the ignition key 11, a battery voltage Bv detected by a battery voltage detecting section 102, phase currents ip of the motor 20 detected by a motor phase current detecting section 103, and a total current it of the motor 20 detected by a motor total current detecting section 104 are inputted into the calculation and control section 110. Electric power is supplied to the motor driving control section 120 from the battery 14 via a power relay 105, and the battery voltage Bv detected by the battery voltage detecting section 102 is inputted into the calculation and control section 110.
The motor driving control section 120 that inputs the q-axis current command value Iq and the d-axis current command value Id, comprises an inverter circuit etc. of an FET bridge circuit that drives the motor 20 after performing controls such as a PI control, a PWM control and so on. Driving currents of three phases are supplied to the motor 20 via motor relays 106 and 107, each phase current ip is detected by the motor phase current detecting section 103, and the detected phase current ip is inputted into the calculation and control section 110 and the motor driving control section 120. The motor relays 106 and 107 are ON/OFF controlled by a driving signal DS from the motor driving control section 120. The total current it which is supplied to the motor 20, is detected by the motor total current detecting section 104. And then the detected total current it is inputted into the calculation and control section 110.
As shown in FIG. 3, since the motor driving control section 120 becomes a current feedback control of the PWM control, with respect to the q-axis current command value Iq and the d-axis current command value Id that are calculated by the calculation and control section 110 based on the steering torque Tr, the velocity Vr, the steering angle θ and the motor angular velocity ω, it is necessary to detect actual motor phase currents Ia, Ib and Ic of the motor 20 by the motor phase current detecting section 103 and feed back in the form of two phases for the vector control. For this reason, the motor phase current detecting section 103 detects the motor phase currents Ia and Ic, since there is a relation of Ia+Ib+Ic=0 with respect to the motor phase currents, a subtracting section 103A calculates the motor phase current Ib based on Ib=−(Ia+Ic), and a three-phase/two-phase converting section 121 collaborates with the steering angle θ to convert the motor phase currents Ia, Ib and Ic into two-phase motor currents iq and id for the feedback control. The motor currents iq and id are fed back to subtracting sections 122q and 122d, respectively. The subtracting section 122q calculates a deviation ΔIq(=Iq−iq) of the q-axis current command value Iq and the motor current iq, and the subtracting section 122d calculates a deviation ΔId(=Id−id) of the d-axis current command value Id (in general, it is Id0) and the motor current id.
The current is controlled so that the deviations ΔIq and ΔId from the subtracting sections 122q and 122d become “0”, the deviations ΔIq and ΔId are inputted into a proportional-integral (PI) control section 123, and PI-controlled voltage command values Vq and Vd are outputted from the PI control section 123. And then, in fact, since it is necessary to apply three-phase current to the motor 20, a two-phase/three-phase converting section 124 collaborates with the steering angle θ to convert the voltage command values Vq and Vd into three-phase voltage command values Varef, Vbref and Vcref. The three-phase voltage command values Varef, Vbref and Vcref are inputted into a PWM control section 125. Based on the voltage command values Varef, Vbref and Vcref, the PWM control section 125 generates PWM control signals that control duty ratios. An inverter circuit 126 comprised of an FET bridge circuit, applies currents to the motor 20 based on the PWM control signals, and applies the motor phase currents Ia, Ib and Ic so that the deviations ΔIq and Δid become “0” to drive the motor 20. The motor relays 106 and 107 are connected between the inverter circuit 126 and the motor 20, and ON/OFF controlled by the ignition key 11 via the calculation and control section 110.
In order to normally stabilize and assist steering operations of a driver, with respect to the battery 14 that is supplied to an electrical control system such as an electric power steering apparatus as described above, it is necessary to maintain the power-supply voltage of the battery 14 in a given and stable range (for example, 10V-15V). However, failures such as the battery degradation (the voltage drop) etc. due to various reasons, occur. Therefore, diagnosis methods and diagnosis apparatuses that are capable of detecting the degradation of the battery and diagnosing the state of the battery before the battery 14 degrades to such a degree that the battery 14 becomes a hindrance to normal driving of the vehicle, are proposed.
As an apparatus that detects the degradation of an automotive battery, for example, an electric power steering apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-28900 (Patent Document 1) comprises two pairs of electric motors that steer wheels, and diagnoses the battery state based on the amount of descent of the battery's terminal voltage when a large current is supplied to these electric motors from a battery. Further, the electric power steering apparatus disclosed in Patent Document 1, drives at least one of a plurality of actuators in a rightward steering direction while driving at least another of the plurality of actuators in a leftward steering direction, and controls output torques of actuators that drive in the rightward steering direction and the leftward steering direction respectively so that wheels are not steered, and further determines the battery state based on the amount of descent of the terminal voltage that a voltage sensor outputs during those actuators drive.
Furthermore, a battery state diagnosis apparatus disclosed in Japanese Patent No. 4270196 (Patent Document 2), comprises a d-axis energizing control means that energizes an electric motor so as to limit only a d-axis armature current in a dq-axes coordinate system which comprises of a d-axis being an action axis of a magnetic flux created by a permanent magnet of a rotor of a brushless DC motor and a q-axis that is perpendicular to the d-axis to less than or equal to a given upper-limit current value and pass the limited d-axis armature current, and not pass a q-axis armature current.